An arterial line blood filter device or “arterial filter” or “blood filter” is one component of an extracorporeal blood circuit, which is used, for example, during cardiopulmonary bypass procedures. The arterial filter removes microscopic sized particles, e.g., microemboli, suspended in oxygenated blood before it re-enters the patient's body. This embolic material has the potential to cause health problems if returned to the patient, and includes (i) particulate matter, such as platelet or white cell aggregates, fat, clots and other foreign matter; and/or (ii) gaseous matter, such as small or large gas (e.g., air) bubbles. Particulate emboli are retained in an arterial filter because their particle size is excluded by the filter's pore size, thereby trapping the emboli and preventing them from continuing in the blood flow into the patient's body. Once the filter has been primed or wetted, fluid covers the filter pores and blocks gaseous microemboli from passing through the pores. Additionally, the gaseous microemboli are cleared from the filter through a vent port in the cap of the filter.
U.S. Pat. No. 5,651,765 discloses one example of an arterial filter. The arterial filter has a housing with a cap portion, a base portion and a generally cylindrical wall portion. The filter element of the arterial filter is disposed within the housing and divides the housing into an inlet chamber in flow communication with a blood inlet and an outlet chamber in flow communication with a blood outlet. The filter element includes a plurality of concentric annular folds, the lengths of which are substantially equal to the length of the wall portion, the folds being supported by a support element. The inner surface of the cap defines an inwardly spiral blood flow path which slopes upward to facilitate removal of gaseous microemboli through a vent port.
In addition to adequately removing embolic material, the priming volume and the pressure drop associated with an arterial filter are also of interest. Arterial filters are generally “primed” before use in order to remove all gaseous matter within the filter. For example, a liquid, such as an isotonic solution, is often introduced into the filter to displace the gaseous matter initially present in the filter. The “prime” volume or “priming” volume of the filter refers to the volume of liquid needed to prime the filter. At the beginning of use, the solution within the filter is displaced by blood, and the solution mixes downstream with the blood. Accordingly, it is desirable to reduce the priming volume of the arterial filter in order to limit the amount of priming solution needed and to limit dilution of the blood before it re-enters the patient. This is especially desirable for arterial filters designed for use with pediatric patients, as the lower overall volume of blood leads to higher dilution than for an adult patient.
As is known, it is also desirable to reduce the pressure drop across the arterial filter in order to prevent hemolysis or other blood trauma. In order to maintain adequate pressure as the blood passes through various components of the extracorporeal blood circuit, a large initial pressure can be required to counteract pressure drops across one or more components. Increasing the overall pressure can lead to blood trauma, for example, as the blood encounters resistance throughout the circuit or from an elevated level of heat generated by the pressurizing pump. In addition, when decreasing the priming volume of an arterial filter, such as for a pediatric arterial filter, it is often also desirable to maintain an elevated flow rate through the filter, which can lead to further efforts to reduce the pressure drop across the arterial filter.